Plywood vs OSB 3

[kaisersoze]

I am looking at a project from another engineer where the roof deck was designed as 5/8" plywood. The client wants to go to 3/4" OSB. My wood books are in a disarray, can anyone post a link to allowable capacities of 3/4" OSB.

Thanks,

Kaiser

 

[kaisersoze]

Let me re-phrase my question. Simply put, what is the lateral capacity difference between 3/4" T&G plywood and 3/4" OSB? I know that plywood has much higher capacity, I just want to know how much. I haven't done wood design in about 4 years, so I can't even remember whe to look for these numbers.

Kaiser

 

[kaisersoze]

Supporting framing are wood trusses @ 16" oc.

Kaiser

 

[frv]

Umm, no.

OSB is actually stiffer as both shearwall and diaphragm. Capacity (or, more precisely, reference nominal unit shear capacity), for the same thickness is exactly the same for OSB and Plywood.

 

[kaisersoze]

frv,

thanks for the quick responce. Where would I find shear values for both. I know they differ for the nail spacing and blocked/unblocked but say an idiot like me wants to see the plywood allowable values and OSB values, where would I look.

Plus, from your comment it appears that OSB=Plywood for same thickness in shear, is that right?

Kaiser

 

[frv]

Look at the NDS SDPWS, Tables 4.2A, 4.2B (OSB), A4.2A and A4.2B (Plywood).

The tables are exactly the same, save for the Ga values.

And yes, for the same thickness, the nominal capacity is the same. Keep in mind that the table lists nominal (not allowable) capacity, so you must apply your safety (or phi) factor.

 

[OldPaperMaker]

You will find the allowable shear values in the Chapter 23-Wood of the International Building Code (IBC), in the AF&PA Supplements or in the APA-The Engineered Wood Association material.

The Panel Grades for shearwalls & diaphragms are APA Structural 1. APA Rated Sheathing or APA Rated Sturd-I Floor. The panels can be manufactured from OSB or plywood. As long as the panels have the same Grade Stamp they are interchangable (but I wouldn't mix them on the same job). The engineer calls out the nail size, panel thickness and nominal width of framing and the codes give you the allowable shear in pounds per lineal foot.

I hope that this helps.

 

[msquared48]

kaisersoze:

Double posting for the same information is not allowed. I am redflagging the post in the wood forum. Please keep this in mind in the future.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[kaisersoze]

Mike,

Apologies for the double posting, I wasn't aware.

Kaiser

 

[msquared48]

No worries...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[dhengr]

They don’t want you walking away from here with the possibility of twice as much information than what you deserve, so you shouldn’t double post. You can just imagine what they think of triple posting. Mike once asked a question about a wood frame with three posts, and he was banned for a year. So, if you want to double post, you should do it within the same thread, so as to conceal your evil intentions.

They don’t want you walking away from here with the possibility of twice as much information than what you deserve, so you shouldn’t double post. You can just imagine .....

 

[boo1]

http://www.apawood.org/level_c.cfm?content=pub_tch_libmain

Form TT-047

 

[kaisersoze]

dhengr....deja vu brother, deja vu

Kaiser

 

[racookpe1978]

Yeah I clicked on the same thread twice one time - Caught a bad case of deja view.

 

[kaisersoze]

frv, OPM, boo: Gracias much for the responses. This forum has been very helpful.

So in conclusion, OSB, Plywood, Composite panels all have identical properties in shear and gravity loading provided they are the same grade.

Kaiser

 

[frv]

Capacity, yes. Stiffness, No. OSB is stiffer.

 

[jaypartain]

As an aside, I would not use T&G plywood for anything but a floor. APA recommends using a 1/8" gap between panel edges for a roof, which is usually achieved through the use of ply-clips. This allows for expansion of the wood panel.

Jason A. Partain, P.E.

http://www.myconstructionfinds.blogspot.com

 

[CANPRO]

Here is a link to the US Dept. of Agriculture Wood Handbook..it has alot of useful info on wood products

http://www.woodweb.com/Resources/wood_eng_handbook/wood_handbook_fpl_2010.pdf

 

[dik]

dhengr... another star... must be a slow day for Mikey... I sometimes double post because you may not find the expertise in the 'obvious' fora...

Dik

 

[MiketheEngineer]

Just make sure that either is APA rated. There are some knock off imports out there....